jeffrey steinberg is the medical director of the fertility institutes in los angeles and new york city. >> we have chromosome 21 lit up in red. >> reporter: the team uses an expensive high-tech approach to select sex. it's called preimplantation genetic diagnosis or pgd for short. >> the accuracy in our program has been 100%. we're on thousands of cases now. we have never, ever missed a correct gender. >> reporter: in his lab, fertilized embryos are genetically analyzed. only those with the desired sex rim planted into the mother's uterus. dr. steinberg says a growing number of couples from the bay area use his services. >> the numbers keep going up and up and up. >> reporter: dr. steinberg says in his experience just as many want a girl as a boy. even so, the use of the technology troubles dr. marcy darnofski. >> now we have a way to do it. the question is, should we? >> reporter: she is associate director at the center for genetics in society in berkeley. she says when a couple spends thousands of dollars to produce a boy or a girl, they want results. >> what if the child doesn't mee